1. Field of the Invention
The present invention relates to a novel fluorine-containing epoxy acrylate resin and fluorine-containing epoxy methacrylate resin (hereinafter referred to inclusively as "fluorine-containing epoxy(meth)acrylate resin"), a process for preparing the same and an adhesive composition containing the fluorine-containing epoxy(meth)acrylate resin. More particularly, the adhesive composition provided by this invention has a refractive index which may be controlled to a desired value, and forms a cured mass excellent in adhesiveness and mechanical properties. A more characteristic merit of the adhesive composition of the invention resides in that the fluorine-containing epoxy(meth)acrylate resin contained as a curable component is cured at room temperature within a short time under irradiation with an UV (ultraviolet) ray.
2. Prior Art Statement
With the progress of the optical communication systems, epoxy resins have been increasingly used in the instruments used in such systems. To improve the adaptability of the epoxy resins for such applications, it is requested that the epoxy resins used for such purpose should have the following properties:
(1) The resin should have a low refractive index to match with the refractive index of an optical member made of glass or a like material; and
(2) The resin could be cured at a low temperature to obviate adverse influences of heating on the optical members otherwise occurred if the resin would be cured at a high temperature during the operation for curing the resin for binding the optical members.
U.S. Pat. No. 4,591,627 discloses an adhesive composition composed of a fluorine-containing epoxy resin, a reactive diluent containing fluorine and a hardner or curing agent containing fluorine. The adhesive composition taught by this prior patent has a refractive index which may be discretionally selected within a range of from 1.415 to 1.57, and is improved in thermal stability and adhesiveness. The merit achieved by the use of the composition as an adhesive for binding optical members, such as glass fibers or optical glasses, is remarkable due to its adaptability for matching the refractive index with those of the associated optical members. However, the adhesive composition taught by this reference cannot be cured at room temperature, the condition required for curing the same being 90.degree. C. for 4 hours or 60.degree. C. for 15 hours. On the other hand, it has been known in the art that an epoxyacrylate resin introduced with an ethylenically unsaturated group is excellent in adhesiveness and resistance to heat. It is also known that such a known epoxyacrylate resin has a photosensitivity due to the presence of the ethylenically unsaturated group, and may be cured at room temperature upon irradiation with an UV ray. Making use of this advantageous property, the epoxy acrylate resins introduced with ethylenically unsaturated groups have been used as photo-curable adhesives or in photo-curable paints. However, these known epoxy acrylate resins have refractive indices of from 1.53 to 1.60 which are substantially equivalent to those of the ordinary epoxy resins containing no fluorine atoms.